In an internal combustion engine for a vehicle, the combustion energy includes kinetic energy and heat energy. This heat energy is utilized for warming an interior of the vehicle and a catalyst. Engine waste heat is recovered through engine coolant.
JP-U-02-96476A and Japanese Patent No. 2909219, for example, describe that an ignition timing and valve timings of intake/exhaust valves are controlled to increase the engine waste heat quantity, whereby a warming-up of the engine and the catalyst is accelerated.
If the ignition timing and/or the valve timing is varied in order to increase the engine waste heat quantity without respect to an engine driving condition, it is likely that a brake thermal efficiency may be excessively deteriorated due to an increase in the engine waste heat. That is, an engine operating region in which the engine waste heat is efficiently utilized is restricted to a specified engine operating region. If a current engine driving condition is out of the specified engine operating region, the brake thermal efficiency may be largely deteriorated. In the above patent documents, there is no description about restricting deterioration in brake thermal efficiency (deterioration in fuel economy) due to an increase in waste heat.